Growing Japanese Maples in containers is a long term project. The maples can live to be over 100 years old. The Japanese consider them ancestral and pass the trees from generation to generation. Japanese maples are the very best of trees for container gardening. With the incredible diversity of color and form, their slow growth habit, and shallow fibrous roots, all but the largest and most vigorous are suited to container gardening.
Because of the shallow fibrous root system maples will do best in a container at least as wide as it is tall. I prefer the look of a container that is wider than tall. This also provides stability and an area to plant companion plants. Finding a container that is durable against the elements will prevent unnecessary repotting. Consider the weight of the container as well. Although we love the look of ceramic, the weight is very difficult when the time comes to root prune or move the container. I have been using Polyethylene bowl containers for my trees as an alternative to ceramic for the last 5 years. These containers are not damaged by extremes in heat or cold, and have the appearance of stone or ceramic without the weight. I also have had trees in well constructed redwood boxes for over 10 years, through several root prunings, with only the bottoms replaced. It is beautiful how the character of the wood evolves as the tree matures.
Maples do best in a well drained acid soil. Most bark based commercial soil mixes with peat moss are suitable. The use of compost, manure or garden soil other is not recommended because of the potential introduction of bacteria or fungus. If your water is heavy in minerals, or alkaline, try to find a potting soil created for azalea and camellia. This will provide the correct Ph level in the container. Excellent drainage is the most important criteria.
Maples need very little fertilizer. The healthiest tree with the most beautiful structure will be achieved by using a high quality liquid fertilizer such as DynaGrow ‘Grow’ at ½ the recommended minimum rate. Fish emulsion has also provided excellent results. Using a fertilizer with low nitrogen, preferably slow release, low residual salts and micro nutrients will provide you the slow grow needed to create a beautiful container tree and maintain the health of the tree over the years.